1. Field of the Invention
The present invention relates to a flash drying apparatus for crushing and drying a raw material containing moisture.
2. Description of the Prior Art
A conventional flash drying apparatus is constructed as shown in FIG. 1. The flash drying apparatus has an enclosure 5 composed of a plurality of cylindrical or truncated conical members coupled together. In a lower portion of the enclosure 5 is provided an inlet 1 through which a hot wind supplied from a hot wind source (not shown) is fed into the enclosure 5. Above the inlet 1 is provided a crushing rotor 12 that is driven to rotate by a driving motor 10 through a belt 14.
The crushing rotor 12 has a plurality of stirrup-shaped hammers 4 that face the inner wall of the enclosure 5, constituting a crusher 3 in which a raw material is crushed as the hammers rotate. Above the crusher 3 is provided a material feeder 9 through which the raw material is fed in. The material feeder 9 is provided with a screw feeder (not shown) so that the raw material stored in a hopper (not shown) or the like is fed out through an outlet 9b so as to fall into the crusher 3.
In an upper portion of the enclosure 5 is provided a classifier 6 that classifies a powdery or granular material. The classifier 6 has a plurality of classifying blades 13 that are made of thin plates, arranged radially, and driven to rotate by a driving motor 8. As shown in FIG. 2, the classifying blades 13 are each arranged with a predetermined inclination a relative to a center line 6a. 
This arrangement serves to keep the rotation speed of the classifying blades 13 at an appropriate rate and simultaneously limit entry of the powdery or granular material into the classifier 6. Above the classifier 6 is provided an exhaust duct 7 that is sucked by a blower (not shown) to permit the powdery or granular material to be exhausted together with air and water vapor.
In this flash drying apparatus constructed as described above, a raw material containing moisture is supplied from the material feeder 9 in such a way as to fall onto the crushing rotor 12 that is driven to rotate by the driving motor 10. The raw material, originally in the form of clusters, collides with the hammers 4, and is thereby crushed into a powdery or granular material. This powdery or granular material is blown upward from under the hammers 4 by a hot wind introduced through the inlet 1 into the enclosure 5, and is thereby, while flowing upward inside the enclosure 5, further dispersed and dried.
On the other hand, the classifying blades 13 that are driven to rotate by the driving motor 8 produces a vortex air stream. The powdery or granular material having flown upward inside the enclosure 5 and come close to the classifier 6 is acted upon simultaneously by the centrifugal force of this vortex air stream and by the centripetal force of the air and water vapor being exhausted. The insufficiently dispersed portion of the powdery or granular material is acted upon more by the centrifugal force, and is therefore thrown out of the classifier so as to fall onto the crusher 3 and be exposed to the hot wind once again.
The powdery or granular material thus dispersed and dried once again is acted upon more by the centripetal force, and is therefore permitted to enter the classifier 6 through the gaps 6b between the classifying blades 13. The powdery or granular material is then exhausted through the exhaust opening 7a of the exhaust duct 7 in the form of dry powder or granules of uniform particle size.
When the raw material is slurry or liquid, i.e. a mixture of a powdery or granular material with a large amount of water, the material is usually formed into cakes using a filter press before being supplied. In less usual cases where such a raw material is supplied as it is, i.e. in the form of slurry or liquid, it is fed in through a pipe provided in the material feeder 9 in such a way as to flow down onto the crushing rotor 12. Then, the raw material, acted upon by centrifugal force, moves outward and makes contact with the hammers 4. Thus, the raw material is dispersed and formed into liquid droplets, and is then dried by the hot wind.
However, in this conventional flash drying apparatus, the raw material, containing moisture, tends to be deposited on the inner wall of the enclosure 5. In particular, the portion of the raw material that falls along the inner wall of the enclosure 5 makes contact with the top surfaces of the stirrup-shaped hammers 4 at the same portion thereof. As a result, this portion of the raw material is not dispersed uniformly, but is scattered, before being subjected to heat exchange with the hot wind, in such a way as to be deposited on the inner wall of the enclosure 5 at about the same portion thereof above the hammers 4.
As this deposit grows, there is a risk of an unduly great pressure loss, or clogging of the passage inside the enclosure 5, which makes the flash drying apparatus unusable. On the other hand, simply increasing the amount of supplied hot wind causes the powdery or granular material having entered the classifier 6 to collide with the classifying blades 13 and be thereby deposited thereon. This, similarly, may lead to clogging of the gaps 6b between the classifying blades 13, causing an unduly great pressure loss.
In cases where the raw material is slurry or liquid containing a large amount of water and is fed in through a pipe so as to flow onto the crushing rotor 12, the raw material, acted upon by centrifugal force, flows outward along strip-shaped paths on the top surface of the crushing rotor 12. Thus, the raw material makes contact with the hammers without being sufficiently dispersed. This causes the raw material to be dispersed in the form of comparatively large drops and thus deposited on the inner wall of the enclosure 5 without being dried. As this deposit grows, clogging of the passage inside the enclosure 5 may result.
An object of the present invention is to provide a flash drying apparatus that can prevent degradation in performance resulting from deposition of a raw material.
Another object of the present invention is to provide a flash drying apparatus that can satisfactorily dry even a raw material in the form of slurry or liquid containing a large amount of water.
To achieve the above objects, according to the present invention, a flash drying apparatus for drying a material containing moisture is provided with: a vertical, cylindrical enclosure; a crusher, composed of a rotating plate-shaped member and a crushing member provided integrally therewith, and disposed in a lower portion of the enclosure, for crushing the raw material into a powdery or granular material; a material feeder for feeding the raw material to the crusher by letting the raw material fall onto the crusher; a hot wind feeder for feeding a hot wind to the powdery or granular material from under the crushing member; a classifier for classifying the powdery or granular material blown upward inside the enclosure by the hot wind; and an exhauster for exhausting the classified powdery or granular material through an upper portion of the enclosure. Here, the crushing member is composed of a plurality of blades made of thin plates, arranged radially above the plate-shaped member, and supported by being coupled to a ring-shaped member provided substantially parallel to the plate-shaped member.
As described above, according to the present invention, the blades are made of thin plates, and are supported by being coupled to the ring-shaped member. This helps reduce the amount of raw material that falls onto the blades and then remains deposited thereon, and thereby restrain the growth of the deposit on the inner wall of the enclosure. Moreover, an air stream passage is formed that permits the air above the crusher to flow from the inside to the outside through the gaps between the blades. This permits the powdery or granular material to be dried repeatedly and thus more fully.
Moreover, the ring-shaped member prevents the blades from being inclined by centrifugal force, and thus permits the blades to be made higher. This helps increase the length of time for which the raw material is crushed while being exposed to the hot wind. Thus, it is possible to disperse the powdery or granular material more fully than ever immediately after the crushing thereof, and thereby further restrain the deposition of the powdery or granular material on the inner wall of the enclosure in a portion thereof above the blades.